1. Field of the Invention
The present invention relates to a thermal head, a printer, and a manufacturing method for the thermal head.
2. Description of the Related Art
There has been conventionally known a thermal head for use in thermal printers, which performs printing on a thermal recording medium by selectively driving a plurality of heating resistor elements based on printing data (see, for example, Japanese Patent Application Laid-open No. 2009-119850). In the thermal head disclosed in Japanese Patent Application Laid-open No. 2009-119850, an upper substrate is bonded to a support substrate having a concave portion so as to close the concave portion, to thereby form a cavity portion between the upper substrate and the support substrate, and heating resistors are disposed on the surface of the upper substrate in positions opposed to the cavity portion. In the thermal head, the cavity portion functions as a heat-insulating layer of low thermal conductivity to reduce an amount of heat to be transferred from the heating resistors toward the support substrate, to thereby increase thermal efficiency and reduce power consumption.
However, if a bonding failure part (void) is generated in a bonding surface between the upper substrate and the support substrate due to air confined therein or fine particles, the upper substrate may be broken or peel off because of its small thickness during the use in a printer, leading to a problem of decreased reliability. Further, such a void is responsible for lowering manufacturing yields. Besides, thermal printers require lower driving voltage and power saving aimed at long-term use, and hence the thermal head is expected to have much increased printing efficiency.